Taraxacum sect. Erythrosperma in Slovakia. Part II. Notes on distribution and ecology of Taraxacum danubium

1 Department of botany, Institute of Biology & Ecology, Faculty of Science, P. J. Šafárik University, Mánesova 23, SK-041 54, Košice, Slovakia, dudas.mato@gmail.com 2 Administration of the Slovak Karst National Park, Hámosiho 188, SK-049 51, Brzotín, Slovakia; robert.suvada@sopsr.sk 3 Department of Botany, Faculty of Science, Palacký University Olomouc, Šlechtitelů 27, CZ-783 71, Olomouc, Czechia; lubos.majesky@upol.cz; radim.vasut@upol.cz 4 Department of Biology, Faculty of Education, Palacký University Olomouc, Purkrabská 2, CZ-779 00, Olomouc, Czechia


Introduction
The genus Taraxacum Wigg. is taxonomically very complicated genus divided into ca. 60 sections, which represent systematic groups or supposed phylogenetic lines and at the same an important taxonomic structure of the genus. In Central Europe, ca. 10 sections are known with more than ca 300 species, of which only five (T. bessarabicum, T. erythrospermum, T. linearisquameum, T. pieninicum and T. serotinum) are sexual (Trávníček et al. 2010). One such section present in the central European region, is a group of xerothermic taxa Taraxacum sect. Erythrosperma (H. Lindb.) Dahlst. (lesser dandelions). The section accommodates only one diploid sexual species (T. erythrospermum Andrz.) and approximately 150-200 polyploid apomictic species (Doll 1973;Vašut 2003;Euro+Med 2006-2019. In Slovakia, the genus Taraxacum is represented by nine sections, namely the sect. Alpestria, Alpina, Dioszegia, Erythrocarpa, Erythrosperma, Hamata, Palustria, Piesis, and Taraxacum. The sect. Erythrosperma is the second most frequent group of dandelions in Slovakia. Although sect. Palustria is species richer than the sect. Erythrosperma, the wet habitats where the species typically occur, are less frequent than xerothermous habitats. The sect. Erythrosperma would require a detailed survey and taxonomic study within the region of Slovakia as such work is still missing, and although lesser dandelions were studied by several authors, these studies merely focused either on small areas (e.g. Richards 1970;Šuvada 2010;Dudáš 2014) or particular species (Schmid et al. 2004;Vašut & Trávníček 2004;Vašut et al. 2005;Vašut & Majeský 2015;Kirschner et al. 2019). The only published list of species is the one of Kirschner & Štěpánek (1995), which is however outdated. This list mentions ca. 15 species for Slovakia, however due to ongoing research this number will increase in future as several well definable but still undescribed apomictic taxa are known from Slovakia (Dudáš and Vašut, unpublished data).
In this paper, which represents the second part of the miniseries dealing with the distribution of Taraxacum sect. Erythrosperma in Slovakia (Dudáš 2019), we want to introduce one of the three most common apomictic species of the section, Taraxacum danubium A. J. Richards. The paper summarizes the present knowledge on the distribution, biology and ecology of the species.

Materials and Methods
The study was carried out during the years 1999-2019. The distribution is based on our field observations as well as on research of herbarium specimens from the following public herbaria collections in Slovakia (BRA, KO, NI, SAV, SLO), Czechia (BRNM, BRNU, MMI, OL, OLM, PR, PRA, PRC), Richards' type collection deposited in Great Britain (OXF) and from private herbarium collection of Jaroslav Zámečník (Hradec Králové, Czechia) and Zdeněk Kaplan (Průhonice, Czechia). Abbreviations of public herbaria follow Thiers (2020+). Herbarium documents from our field course are deposited in KO (M. Dudáš, R. Šuvada; specimens are fully digitalized and available upon request) and in OL (R. J. Vašut, Ľ. Majeský, M. Dudáš). A list of revised specimens and literary records are provided in Appendix 1. The map was designed in the program ArcGis, version 9.2. The mapping grid follows the grid template described by Niklfeld (1971). The taxonomy and nomenclature of Taraxacum follow Štěpánek (1995) &Vašut (2003). Names of syntaxa follow Jarolímek et al. (2008.

Distribution in Slovakia
Taraxacum danubium A. J. Richards, Acta Fac. Rer. Nat. Univ. Comen. ser. bot., 18: 108, 1970 [syn. T. austriacum var. danubium (A. J. Richards) R. Doll Feddes Repert. 84: 21, 1973.] is one of the most common species of the section Erythrosperma in the western part of Slovakia. However, it is by far not as common as T. erythrospermum or T. parnassicum (Dudáš, unpublished data). Especially, the species is common on blown sands of the Záhorská nížina lowland and limestone rocky sites in the Biele Karpaty Mts. and Strážovské vrchy Mts. Towards the east, the species is gradually vanishing and becoming rare. The main distribution range of T. danubium thus lies in western Slovakia.
We recorded the presence of species in 19 phytogeographic districts and subdistricts (out of 31). Most of them are situated in the area of the Carpathian flora (Carpaticum) (over 33 sites in 12 districts) while less in the area of the Pannonian flora (Pannonicum) (over 30 sites in 7 districts) as showing distribution map (Fig. 1.).
Within the Pannonicum (Záhorská nížina lowland, Podunajská nížina lowland and Devínska Kobyla Hills) the species shows preferences for the warmest regions with sandy soils. The most of localities are present at lower altitudes (130-250 m). Within the Carpaticum the species is growing in higher altitudes (250-920 m). Here it usually occurs on limestone and dolomite rocky outcrops, on touristic sightseeing points, hilltops and castle hillsides (mainly Strážovské vrchy Mts. and Biele Karpaty Mts. less in the Tematínske kopce Mts. and Tribeč Mts.). The abundant occurrence on calcareous rocky sightseeing points between Trenčianske Teplice town and villages of Omšenie and Dolná Poruba, over valley of Teplička River in the Strážovské vrchy Mts. was found. In southern and southeastern parts of Slovakia the number of localities rapidly decreases, and known populations are consisting of a few individuals only. Surprisingly, in the Slovenský kras Mts., an ideal area with many suitable habitats, only five recent populations were discovered. We thus expect to find further new localities in future here.
The overall minimum altitude of ca. 130 m reaches the species in Kopáč Island near Danube River (Pannonicum, Podunajská nížina lowland; herbarium specimen deposited at herbarium SLO). The maximum recorded altitude (910-920 m) reaches the species on the top of Chmeľová hill in the Biele Karpaty Mts. (Carpaticum) on a small limestone ridge. The localities of the species in Poland are situated in low hill area between 200-360 m (Wolanin & Musiał 2018). In Czechia, localities in Moravia are situated in the lowlands and hills (between 180-500 m), and altitudinal maximum reaches the species in the Sedlo hill (České strědohoří Mts.) with 720 m (Vašut 2003;Kirschner et al. 2010). In Hungary and Austria, the distribution prevails in lowlands and low hilly areas; however, it seems that the species occurs only sparsely in Hungary (e.g., Šuvada 2010; herbarium specimens in KO, BRNM, BP and OL). From our survey as well as based on data from Vašut (2003) the region delimited by cities of Bratislava -Wien -Znojmo -Hodonín -Trenčín -Nitra -Bratislava represents the centre of distribution of T. danubium.

Differentiation from other taxa
Although T. danubium is a very remarkable species (Fig. 2), it is not always easily distinguishable from other species of section Erythrosperma. Its typical leaf-shape with patent and narrow lateral lobes, which are usually swollen at apex, and terminal lobes triangular (of outer leaves) or trilobate (of inner leaves) with swollen drop-like apex is very characteristic (Fig. 2A). Achenes are dark brownish-red with body densely spinulose. Pollen is present; the length of irregular grains varies between 17-43 µm.
Not well-developed plants can sometimes be confused with other taxa (Tab. 1). Similar leaf shape can sometimes be seen in diploid T. erythrospermum (which usually has very narrow lateral lobes, strongly toothed lateral margin of lobes and distinct tunica of dried leaves at the base of leaf-rosette). Also young plants of T. parnassicum resemble the leaf pattern of juvenile T. danubium, and these two taxa can be thus confused. However, the presence of pollen and a more regular width of inner bracts (for T. danubium) are safety features for distinguishing these two species. Other similar species is Taraxacum persicum, a rare species known from southern and eastern Slovakia (Chľaba, Soví hrad hill, Viniansky hrad castle), which is differing by narrower lateral lobes (mostly lacking the characteristic drop-like apex) and by absence of pollen (Kirschner & Štěpánek unpublished data). T. erythrospermum present, regular size (rare irregular) usually adpressed regular and triangular (outer leaves) to trilobate and linear (inner leaves); mostly obtuse 3-5 pairs very variable in size and shape, mostly narrow, linear, obtuse at apex and often distinctly denticulate red, small, (2.5-) 3.2-3.0 mm long, cone 0.6-0.8 mm long.
tunica of dried leaves at base of the leafrosette; plants with numerous small capitula, V-shaped at their base

Ecology and habitats
Taraxacum danubium belongs to the most xerothermophilic species of the section Erythrosperma growing on calcareous and sandy dry soils (Trávníček et al. 2010). Our results show that T. danubium in Slovakia prefers mostly limestone's grassy hillsides, rocky outcrops on sightseeing points and castle hills (alliance Festucion valesiacae and Alysso alyssoidis-Sedion albi) and sandy dunes (alliance Festucion vaginatae). Less frequently it grows on lightly trampled sites along tourist paths, on dry pastures (alliance Cynosurion cristati), in light shrubberies (alliance Prunion spinosae) and open oak, pine and birch forests of the alliance Quercion pubescentis-petraeae and Pinetum sylvestris. The occurrence of T. danubium is always accompanied by other species from the section Erythrosperma, especially by T. erythrospermum, T. cristatum, sometimes T. prunicolor and T. parnassicum.

Threats and conservation status
Taraxacum danubium is not endangered in Slovakia. The number of localities and the number of individuals in populations in Slovakia suggests the species is not threatened in near future. Moreover, numerous localities occur in protected areas. Furthermore, many localities represent touristic hotspots, and a high number of tourists provide regular disturbance of soil, which is profitable for the species as a weak competitor (similar also to other species of the section Erythrosperma). Therefore the species is not included into the Red List of endangered species in Slovakia (Turis et al. 2014;Eliáš et al. 2015).